This application is based on French Patent Application No. 01 03 529 filed Mar. 15, 2001, the disclosure of which is hereby incorporated by reference thereto in its entirety, and the priority of which is hereby claimed under 35 U.S.C. xc2xa7119.
1. Field of the Invention
The invention relates to patch antennas. A patch antenna is typically used in a portion of the spectrum including radio frequencies and microwave frequencies and in particular in the GSM, DCS, PCS and UMTS bands.
2. Description of the Prior Art
Most antennas have one resonant frequency band. To transmit, when the antennas are excited in that resonant frequency band by means of a feed line, they support standing electromagnetic waves which are then coupled to electromagnetic waves radiated into space. To receive, the waves take the same forms but travel the above path in the opposite direction. Various antennas of the above type are known in the art.
Using microstrips on a plane as an antenna for transmitting signals is known in the art. Conductive patches are disposed on the upper face of a dielectric substrate and a conductive layer is placed on the lower face of the substrate. The conductive layer then serves as an electrical ground plane. The substrate is typically flat, rectangular and of constant thickness.
A multiband antenna is described in the document FR-A-2 772 518. It includes a flat patch disposed on the upper surface of a dielectric substrate. A ground layer is disposed on the lower surface of the dielectric substrate. This antenna is a quarter-wave antenna because a short circuit conductor disposed on an edge of the dielectric substrate connects the patch to the ground layer. This antenna includes connecting conductors for transmitting signals between the antenna and a signal processor.
A paper presented at the Davos AP 2000 conference by Ollikainen, Kivekas, Toropainen and Vainikainen discloses a multiband antenna including three patches placed on the upper surface of a Styrofoam (registered trademark) substrate. A ground layer is placed on the lower surface of the dielectric substrate. A first patch for the low band is joined to a second patch for the high band. The two patches therefore form a first two-band member having a zig-zag shape and including a feed. The two-band member includes a short circuit in the form of a junction with the ground plane. A third patch is positioned beside the second patch to obtain a double resonance in the high band, with a widened pass-band. The third patch includes a short circuit in the form of a junction with the ground.
The document xe2x80x9cNovel meandered planar inverted F-antenna for triple frequency operationxe2x80x9d published in Microwave and Optical Technology Letters, page 58, volume 27 No. 1, Oct. 5, 2000, describes a multiband antenna which has three patches placed in the same plane as a ground, in a xe2x80x9cmeanderingxe2x80x9d pattern. The three patches have a single feed.
The document U.S. Pat. No. 4,766,440 describes an antenna having two half-wave resonances. The antenna includes a rectangular patch in which the resonance paths are respectively established in the directions of the width and the length of the patch. A U-shaped slot is formed in the patch and does not reach the edges of the patch. The patch is connected to a coupling system including impedance converter means. Impedance conversion matches the coupling system to the various resonant frequencies used.
The document U.S. Pat. No. 4,771,291 describes an antenna including a patch. The patch includes localized short circuits and straight slots formed in the patch that do not reach the edges of the patch.
PCT application FR001586, not published at the date of filing this application, describes an antenna including a conductive patch with a ground, a feed connection, a short circuit connection connecting the patch to the ground, and a sinuous slot formed in the conductive patch.
The document IEEE Antennas and Propagation Society International Symposium Digest, Newport Beach, Jun. 18-23, 1995, pages 2124-2127, Boarg et al, xe2x80x9cDual Band Cavity-Backed Quarter-wave Patch Antennaxe2x80x9d describes an antenna with quarter-wave resonances. A first resonance is defined by the dimensions and the characteristics of the patch and the substrate. A second resonance is obtained by using a matching system.
The above antennas have drawbacks. On the one hand, they necessitate large flat patches, incompatible with the small dimensions of the housings of mobile communication apparatus. On the other hand, they necessitate the fitting of capacitive loads to widen the pass-band, which adds to the cost and complexity of the antenna. Furthermore, they have a small bandwidth, in particular in the frequency band dedicated to the UMTS.
The above antennas are also costly and have a low send or receive efficiency. Nor is adjusting the resonant frequencies and the bandwidths of said frequencies a simple matter with these antennas.
There is therefore a need for an antenna that solves the above problems.
The invention therefore provides an antenna including a conductive patch including two sinuous slots, a ground, a short circuit connection connecting the patch to the ground, and a feed connection connected to the patch and having a radiation diagram including a primary resonant band including frequencies from 1 950 MHz to 2 100 MHz and having a width greater than 20%.
In one variant the radiation diagram includes a secondary resonant band including frequencies from 890 MHz to 950 MHz and having a width greater than 10%.
In another variant the patch has a substantially polygonal shape.
In a further variant the slots open onto the same edge of the patch.
In a still further variant the short circuit connection is connected to the patch via the edge onto which the slots open or an adjacent edge.
In one variant the feed connection is connected to the patch via the edge onto which the slots open or an adjacent edge.
In another variant the feed connection and the short circuit connection are disposed on respective opposite sides of at least one of the slots.
In a further variant the slots have contours of different length.
The invention also provides an antenna in which the difference in the lengths of the contours of the slots is from 5% to 30%.
In one variant the ground is a conductive surface parallel to the surface of the patch.
In another variant the distance between the slots is from 5 mm to 15 mm.
In a further variant the patch is formed of a metal film.
In another variant the slots have substantially the same shape and the same orientation.
In a further variant the slots have substantially the same shape and opposite orientations.
The invention also provides radio communication apparatus including an antenna according to the invention and having a thickness less than 20 mm, a length less than 120 mm, and a width less than 50 mm.
Other features and advantages of the present invention will become apparent on reading the following description of embodiments of the invention, which description is given by way of example and with reference to the accompanying drawings.